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Acquired Business and Noncontrolling Interests - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 20, 2017
Sep. 30, 2017
Sep. 30, 2017
Dec. 31, 2016
Sep. 24, 2016
Goodwill   $ 39,914,000 $ 39,914,000 $ 31,134,000 $ 31,134,000
Fletes Avella | Landstar Metro          
Payments to acquire businesses, gross $ 8,199,000        
Business combination, recognized identifiable assets acquired and liabilities assumed, liabilities $ 2,200,000        
Ownership interest acquired by affiliates 30.00%        
Goodwill   $ 8,800,000 8,800,000    
Percentage of goodwill estimated to be deductible for tax purposes   70.00%      
Percentage of goodwill estimated to be deductible after purchase of noncontrolling interests by the company   100.00%      
One-time costs related to completion of acquisition   $ 1,000,000 $ 1,000,000    
One-time costs related to completion of acquisition, per share     $ 0.01    
One-time costs related to completion of acquisition, per share diluted     $ 0.01    
Fletes Avella | Landstar Servicios          
Ownership interest acquired by affiliates 30.00%